SU1750996A1 - Overvoltage protection device for converter of direct current traction substation - Google Patents

Description

voltage. This adversely affects the reliability of its operation.

The purpose of the invention is to simplify maintenance of the protection and increase the reliability of its operation.

The essence of the invention is as follows. A protection device, which has arresters connected through damping resistors to the midpoint of the compensating reactor of the converter being protected, and the diodes, complement the six diodes and form two diode three-phase bridges. Four gaps are connected to the outputs of the bridges, and the inputs of these bridges are connected to the terminals of the valve windings of the converter transformer with a phase shift of 60 zl, degrees. When connecting arrays, their number decreases. This simplifies maintenance, as compared to arresters, diodes are objects that require simpler and less labor-intensive maintenance. Due to the use of three-phase diode bridges connected to the voltage of the valve windings of the converter transformer, which have a phase shift of 60 degrees. The voltage that is applied to the arresters has a pause. In the presence of pauses, the time of current flow after triggering the arrester (accompanying current) and the duration of the arc in it are reduced, conditions for repeated breakdowns of the spark gap of the arrester are not created. As a result, protection works more reliably.

The drawing is a schematic diagram of an overvoltage protection device for a converter.

The protected object consists of a converter transformer 1 with a power winding 2 and two valve windings 3, a balancing reactor 4, a semiconductor (thyristor, diode) converter 5. The valve windings 3, a balancing reactor 4 and a converter 5 are interconnected according to the scheme two reverse stars with balancing a reactor that has terminals 6 for connecting a load (not shown). The converter is powered by a three-phase alternating voltage from the mains, which is not shown in the diagram, and is connected to the terminals of the network winding 2 of the transformer 1.

The protection device has two diode three-phase bridges 7, arresters 8 and damping resistors 9. Each bridge 7 is connected by its input to the terminals of the valve windings 3 of the transformer 1. The voltages of which have a phase shift of 60 electrons. hail.

When powering the bridges 7 with such a three-phase voltage to the discharge capacitor 8, a periodic

a sequence of unipolar voltage pulses that follow with pauses and with the frequency of the mains voltage of the converter. The front and rear edges of these voltage pulses are formed from the half-wave portions of the sinusoids of the voltage of the valve windings 3 of the transformer 1, and from the voltage of the balancing reactor 4. The flat part of the pulses

5 consists of half-wave sections of sinusoids having a phase shift of 60 el. hail, the voltage of the valve windings 3, the amplitude of the pulses is equal to the amplitude of the rectified voltage (the voltage at the terminals 6} of the transducer to be protected. The duration of the pulses and pauses is 5/6 and 1/6 period of the supply voltage converter.

Protection works as follows. In converter operation modes,

5 when overvoltages are absent, voltage pulses are applied to the arresters 8. The amplitude of these pulses is less than the voltage of the sample of the spark gaps of the arresters 8, the spark gaps do not penetrate and the current flows. in the circuit of the damping resistors 9 does not leak.

When any time appears on any of the valve windings 3 of the transformer 1, the overvoltages are dangerous

5 magnitudes the spark gap is punched by the corresponding dischargers 8 and in their

circuits there is a current, the value of which is limited by the resistance of damping resistors 9. When such a current flows

0, the overvoltage energy is dissipated in the resistors 9 and, as a result, the overvoltages are limited to an acceptable level.

After limiting overvoltage

5 under the action of the operating voltage of the valve windings 3 in the circuit of the arresters 8, which limit the overvoltage, the accompanying current flows, the value of which is limited by the resistance

0 damping resistors 9. The accompanying current flows until the pulse voltage applied to the conductive current discharge 8 decreases to zero and a pause begins. After a pause, the co5 conductive current ceases and, during its time, the spark gap of the current-carrying arrester 8 recovers its ability to hold the voltage that is applied to its spark gap during the operation of the converter. After that, the protection device returns to its original state and is ready to re-limit the overvoltages.

The time of flow of the accompanying current is determined by the moment of the appearance of the overvoltages relative to the beginning of the voltage pulses applied to the arresters 8. The closer to the beginning of the pulses (farther from their beginning) is the moment of the appearance of the overvoltages, the longer . But in any case, the flow time of the accompanying current is limited by the duration of the voltage pulse that is applied to the arresters. Such a limitation of the flow time of the accompanying current increases the reliability of the protection device.

Claims (1)

The invention is a device for protection against overvoltages of a converter station of a direct current substation, made according to two reverse stars with a balancing reactor containing four gaps connected through damping resistors to the midpoint of the balancing reactor and connected to the terminals of the valve windings of a transformer with a phase voltage shift of 60 electr., and six diodes characterized by that, in order to simplify maintenance and increase reliability in operation, it is equipped with an additional six diodes with the formation of two three-phase diode bridges, which are connected by their inputs to the terminals of the valve windings of the transformer with zovym shift to 60 e. hail, and outlets - to dischargers. R one